Presentation materials
In superconducting quantum computing a qubit state can be inferred through the measurement of low-power microwave fields. In this context, the large bandwidth and ultralow-noise amplification given by a Travelling Wave Josephson Parametric Amplifier (TWJPA) plays an essential role. In our work we derive a quantum model for an rf-SQUID (rf-Superconducting QUantum Interference Device) based...
One of the fundamental motivations for science and technology is measurement of parameters with extreme precision. Quantum metrology is a significant application of quantum information theory for emerging quantum technologies, which exploits the theories of quantum mechanics, like entanglement, to surpass the limits on measurement and estimation of parameters realized using only classical...
Quantum phenomena are manifestly unpredictable. While classical uncertainty arises from ignorance, quantum uncertainty is intrinsic. Even for pure quantum states that represents the maximal knowledge that one could have about quantum states, we can only make probabilistic predictions. In addition, when the state is mixed, the variance is a hybrid of quantum and classical uncertainties. Another...
We study the localization properties, energy spectra, and coin-position entanglement of the aperiodic discrete-time quantum walks. The aperiodicity is described by spatially dependent quantum coins distributed on the lattice, whose distribution is neither periodic (Bloch-like) nor random (Anderson-like). Within transport properties we identified delocalized and localized quantum walks mediated...
In recent times, nonlocality has been extensively explored for various device-independent certification tasks. Despite the success of these certification schemes towards verifying huge class of states, the avenue for certification of measurements is not well explored. It remains a highly nontrivial problem to propose a device independent scheme which could certify arbitrary pairs of...
The matrix generalizations of Compressed Sensing (CS) were adapted to Quantum State Tomography (QST) previously by Gross et al. [Phys. Rev. Lett. 105, 150401 (2010)], where they consider the tomography of n spin-1/2 systems. For the density matrix of dimension d = 2^n and rank r with r << 2^n, it was shown that randomly chosen Pauli measurements of the order O[dr log(d)^2] are enough to fully...
We study the possibility of using dark solitons in quasi-one-dimensional Bose-Einstein condensates to produce two-level or three-level systems (qudits) by exploiting the intrinsic nonlinear and coherent nature of the matter waves. We calculate the soliton spectrum and the conditions for a qudit to exist. We also compute the coupling between the phonons and the solitons and investigate the...
Micro/nano-fabrication techniques have recently allowed producing quantum devices displaying ultra-strong coupling (USC) of radiation and matter. In this non-perturbative regime, distinctive phenomena emerge, as the highly entangled ground state involving many-photon states of the field. These ground-state virtual photons (VPs) cannot be revealed by standard photodetection since the...
Motivated from the work on distillation of Einstein-Podolsky-Rosen steering by Nery et al, we present a distillation scheme that extracts perfect genuinely steerable assemblages of GHZ/W type from the 'N' partly genuinely steerable assemblages of GHZ/W type by applying free operations. We first introduce free operations in the context of genuine tripartite steering and show that 2W-LOCC and...
We introduce the Multipartite Collision Model to simulate the Markovian dynamics of any multipartite open quantum system by decomposing the system-environment interaction into elementary collisions between subsystems and ancillae, thus providing a simple decomposition in terms of elementary quantum gates for quantum computation. The generality of the model allows for the study of any possible...
This paper proposes a quantum circuit for computing the mean value from a given set of quantum states. The circuit consults a Quantum Random Access Memory to get the values of the set, and by using superposition, interference and entanglement phenomena, it can estimate the mean value in
We assess whether a confined Wigner molecule constituted by 2N fermions behaves as N bosons or 2N fermions. Following the work by Law [Phys. Rev. A 71, 034306 (2005)] and Chudzicki et al. [Phys. Rev. Lett. 104, 070402 (2010)] we discuss the physical meaning and the reason why a large amount of entanglement is needed in order to ensure a bosonic composite behavior. By applying a composite boson...
We advance on the characterization of quantum coherence resource theory, by introducing the notion of coherence vector of a general quantum state. We show that the coherence vector completely characterizes the notions of being incoherent, as well as being maximally coherent. Moreover, using this notion and the majorization relation, we obtain a necessary condition for the conversion of...
The problem of bound entanglement detection is a challenging aspect of quantum information theory for higher dimensional systems. Here, we propose an indecomposable positive map for two-qutrit systems, which is shown to detect a class of positive partial transposed (PPT) entangled states. A corresponding witness operator is constructed and shown to be weakly optimal and locally implementable....
The stabilizer formalism has been developed as a convenient way to describe quantum correction codes, however its utility does not end there. In our study we present a new procedure that one can use to identify a genuinely entangled subspace that is stabilised by some stabilizer. We use this new procedure to derive a bound on the dimension of a stabilised, genuinely entangled subspace. Then,...
Identifying which master equation is preferable for the description of a multipartite open quantum system is not trivial and has led in the recent years to the 'local vs. global debate' in the context of Markovian dissipation. We treat here a paradigmatic scenario in which the system is composed of two interacting harmonic oscillators A and B, with only A interacting with a thermal bath -...
The precise measurement of low temperatures is a challenging yet fundamental task for quantum science. In particular, in-situ thermometry of cold atomic systems is highly desirable due to their potential for quantum simulation. I will present some of our recent work [1] showing that the temperature of a non-interacting Fermi gas can be accurately inferred from the non-equilibrium dynamics of...
Is it possible to reconcile irreversibility and a time-reversal symmetric theory such as quantum mechanics (QM)? In this work, we consider a specific type of constructor-based irreversibility, which allows a generalization of the classical irreversibility based on the second law of thermodynamics. Let the task T be the specification of a physical transformation on qubits which brings a quantum...
We have experimentally performed joint measurements of the four polarization orientations that maximally violate a Bell's inequality. The joint statistical distributions directly obtained with the joint measurements depend on the measurement uncertainty trade-off between the two complementary polarizations measured for each photon. Our experimental results show that the Cirel'son bound is the...
Some experiments already have shown signatures of many-body localization (MBL) in the disordered Bose-Hubbard model in one and two dimensional ultra cold atomic lattice gases [1] as well as the related superfluid to Bose-glass transition in three dimensions for moderate disorder [2]. A proper theoretical understanding of the MBL phenomenon depends on knowledge about the full eigenstate...
Machine learning methods have proved to be useful for the recognition of patterns in statistical data. The measurement outcomes are intrinsically random in quantum physics, however, they do have a pattern when the measurements are performed successively on an open quantum system. This pattern is due to the system-environment interaction and contains information about the relaxation rates as...
Memory effects in open systems dynamics have been the subject of significant interest in the last decades. Methods quantifying this effect, however, are often difficult to compute and lack analytical insight. With this in mind, we consider Gaussian collisional models, where non-Markovianity is introduced by means of interactions between neighboring environments. We show that the dynamics can...
Quantum systems can only be measured by interactions with an external meter. This interaction is described by a unitary transformation that involves quantum superpositions in both the system and the meter. In this presentation, we analyze the sensitivity of the quantum coherent meter response using the Fisher information. It is shown that the sensitivity of the meter is limited by quantum...
We address the propagation of Gaussian states of light in optical media with a finite bandwidth. Upon assuming weak coupling and low temperature we show that attenuation (damping) is strongly suppressed and that the overall diffusion process may be described by a Gaussian noisy channel with variance dependening only on bandwidth.
Discrete-time quantum walks (DTQWs) are known to exhibit exotic topological states and phases. Physical realization of quantum walks in a noisy environment may destroy these phases. We investigate the behavior of topological states in quantum walks in the presence of a lossy environment. The environmental effects in the quantum walk dynamics are addressed using the non-Hermitian Hamiltonian...
Recently, there has been much interest in the efficient preparation of complex quantum states using low-depth quantum circuits, such as Quantum Approximate Optimization Algorithm (QAOA). While it has been numerically shown that such algorithms prepare certain correlated states of quantum spins with surprising accuracy, a systematic way of quantifying the efficiency of QAOA in general classes...
Randomness appears both in classical stochastic physics and in quantum mechanics. In this work, we address a computational scenario of shared randomness processing where quantum sources manifest clear-cut precedence over the classical counterpart. For proper apprehension of the quantum advantage we formulate a resource theoretic framework for shared randomness processing. The advantage is...
Quantum entanglement plays important roles in many areas of quantum information processing (QIP). Nevertheless, quantum entanglement is not the only form of quantum correlation that is useful for QIP. In fact, some separable states may also speed up certain quantum tasks, relative to their classical counterparts. Example of such quantum correlations, is a quantity, called quantum discord (QD),...
Information is physical but information is also processed in finite time. Where computing protocols are concerned, finite-time processing in the quantum regime can dynamically generate coherence. Here we show that this can have significant thermodynamic implications. We demonstrate that quantum coherence generated in the energy eigenbasis of a system undergoing a finite-time information...
Fault-tolerant universal quantum computers still appear to be more than a decade away. However, consistent growth in the field of quantum technologies over the years has lead to the development of Noisy Intermediate-Scale Quantum (NISQ) devices. The computational capabilities of these devices are considerably restricted due to limited connectivity, short coherence time, poor qubit quality and...
This work provides the unconditional security of a semi quantum key distribution (SQKD) protocol based on 3-dimensional quantum states. By deriving a lower bound for the key rate, in the asymptotic scenario, as a function of the quantum channel's noise, we ?nd that this protocol has improved secret key rate with much more tolerance for noise compared to the previous 2-dimensional SQKD...
Reference frames are of special importance in physics. They are usually considered to be idealized entities. However, in most situations, e.g. in laboratories, physical processes are described within reference frames constituted by physical systems. As new technological developments make it possible to demonstrate quantum properties of complex objects an interesting conceptual problem arises:...
Resolving the separation between the incoherent point sources is one of the important problems in optical imaging. The most conventional direct imaging approach is limited by the so-called Rayleigh criterion, which restricts the resolution of two point sources if their diffraction patterns overlap significantly. Here, we explore the advantage of the array homodyning in resolving the separation...
We study the existence and charaterization of self-trapping phenomena in discrete-time quantum walks. By considering a Kerr-like nonlinearity, we associate an acquisition of the intensity-dependent phase to the walker while it propagates on the lattice. Adjusting the nonlinear parameter (χ) and the quantum gates (θ), we will show the existence of different quantum walking regimes, including...
We are interested in quantum features of acetylcholine (ACh) and its complexes, because ACh is a prominent neurotransmitter of the peripheral and the central nervous system. The synaptic release of ACh, called cholinergic transmission, is widespread, occurring centrally, deep in the cortex, and in the distal periphery, where motoneurons contact muscles. The density functional theory (DFT) was...
Electronic spin degrees of freedom provided by spin ensembles have been efficiently exploited into circuit quantum electrodynamics architectures based on microwave devices and resonators at low temperature. Molecular spins have recently emerged as a new class of quantum systems whose electronic and nuclear spin states and their related quantum features can be tailored synthetically. Different...
Decoherence is a fundamental obstacle to the implementation of large-scale and low-noise quantum computing devices. In the present work, we investigate the role of the fidelity of finite-dimensional quantum systems in the context of their robustness to decoherence. We suggest an approach for suppressing errors by employing pre-processing and post-processing unitary operations, which precede...
Photosynthesis is a highly efficient process, nearly 100 percent of the red photons falling on the surface of leaves reach the reaction center and get transformed into energy. Quantum coherence has been speculated to play a significant role in this very efficient transport process which involves photons transforming to excitons and then traveling to the reaction center. Studies on...
The fault-tolerant regime allows a quantum computer to perform a quantum algorithm with arbitrary precision. To do so it is necessary to perform all single-qubit and two-qubit entangling gates with a low enough infidelity. In the context of trapped-ion quantum computing, operations based on microwaves are an alternative to the more diffused laser driven operations. Due to their lower...
Low-particle systems constitute a direct link between the physics of one or two bodies and the physics of many bodies. This connection has important consequences related to the collective properties that originate in the interactions between particles and in the statistic that governs them. We study a system consisting of independent molecules formed by two distinguishable fermions that...
In adiabatic quantum computation, the goal is to find the ground state of a many-body Hamiltonian starting from the simple ground state of a transverse field potential. A fast evolution time renders the system robust against decoherence and thermal noise but can cause diabatic transition towards excited states. Adding a counterdiabatic (CD) potential to the original Hamiltonian can suppress...
Microscopic systems driven out of equilibrium and put in contact with thermal reservoirs act as prototypes of stochastic cyclic heat engines [1,2]. In these engines, thermal fluctuations of heat, work and entropy production cannot be neglected, and the concepts of classical thermodynamics need to be generalized to microscopic nonequilibrium regime [3]. Employing the theoretical framework of...
